Been reading about the 'jaw fatigue' problems.
My solution was to have a mouthpiece that you all but had to
force into your mouth. (The one my now-ancient USD Calypso
III came with worked fine.) That way you didn't need to
'hold' it in place -- it just stayed there. The tabs were
for biting down on to get temporary, extra holding power
(like when those octopussies try to rip it away!).
A number of us then-dive-instructors could not come up with
ANY reason to take the regulator out of your mouth during a
dive (even if you barf, keep the regulator in place! -- But,
don't eat chicken or any 'chunky' food before diving, 'cuz
the chunks can't get out the exhaust port and might jam it
open!)
(Mmmmmm..., chicken!!!)
Good luck!
makuabob (a.k.a. Bob Dayle)